The conflict of treating psychosis in Parkinson’s disease

One of the main challenges of treating psychotic symptoms in PD is that many antipsychotic medications have an anti-dopaminergic effect, i.e., they block the action of dopamine.¹ In doing so, antipsychotics counteract the action of levodopa and can worsen the control of motor symptoms.¹ Patients are therefore caught ‘between a rock and a hard place’, feeling unable to take antipsychotic medications without incurring a worsening of physical symptoms.¹ Newer drugs can be effective in treating psychotic symptoms, but with a less potent dopamine-blocking action.¹ These are sometimes referred to as ‘atypical antipsychotics’.³

The symptoms of psychosis are thought to be more complex than aberrant dopamine signalling.⁴ In patients with PD, there is evidence for acetylcholine and serotonin signalling, as well as dopamine neurotransmission, being involved in the pathophysiology of psychosis.³

References:
1. Divac N, Stojanović R, Savić Vujović K, et al. The efficacy and safety of antipsychotic medications in the treatment of psychosis in patients with Parkinson’s disease. Behav Neurol 2016; 2016: 4938154.

2. Braak H, Ghebremedhin E, Rüb U, et al. Stages in the development of Parkinson’s disease-related pathology. Cell Tissue Res 2004; 318 (1): 121–134.

3. Samudra N, Patel N, Womack KB, et al. Psychosis in Parkinson disease: a review of etiology, phenomenology, and management. Drugs Aging 2016; 33 (12): 855–863.

4. Rolland B, Jardri R, Amad A, et al. Pharmacology of hallucinations: several mechanisms for one single symptom? Biomed Res Int 2014; 2014: 307106.